1. Technical Field
The present application relates to a communication control apparatus, and in particular to a communication control apparatus for common bus connection devices such as a Universal Serial Bus (hereinafter USB) device used in a USB device controller or the like.
2. Related Art
Recently, data transmission lines for communication have been developed with progress of computer technologies and public communication networks such as the Internet. As an example, communication control apparatuses for Transmission Control Protocol (hereinafter TCP), Internet Protocol (hereinafter IP) and the like have been proposed and they are used in practice. Conventionally, USB has been proposed as a standard for common data transmission lines to connect a peripheral device such as a keyboard, mouse, modem, or joy stick to a personal computer.
USB as a common bus was initially introduced as USB 1.1 which is a standard for connecting devices that do not communicate so many amounts of data with a main unit. However, while development of IEEE 1394 has been delayed that was initially contemplated as a high-speed serial interface, USB 1.1 has seen explosive growth so that it has transferred to an interface also being capable of connecting with CD-R, HDD and the like. However, since USB 1.1 was a standard for transferring data only at maximum rate of 12 Mbps (=1.5 MB/s), USB 2.0 (HI-SPEED USB) standard has been developed in order to meet the need for high speed data transfer.
In the above USB standard, it is required to save power consumption of USB devices including an internal USB device controller, since there are bus power devices operating with power supply from a USB host device. Also in the USB standard, suspend mode is defined for saving power consumption of the entire system. This mode involves recognizing suspend (drive stop) if a packet communication from the USB host device to the USB device does not occur for 3 ms or more, and during the suspend period, the USB device controller can stop an internal clock or a clock itself being provided.
In the prior art described in National Publication of International Patent Application Lied-open No. 2001-506788, since the USB device controller performs power saving of itself and peripheral circuitry only during a suspend period of the USB standard, it is not achieved to save power consumption according to transfer states in normal transfer mode other than the suspend period.
In the conventional communication control apparatus for common bus connection devices described above, power saving of the control apparatus and the peripheral apparatus is performed only during for example the suspend period of the USB standard, therefore it is not achieved to save power consumption according to transfer states in normal transfer mode other than the suspend period.